Mobile or wireless communications networks are capable of carrying both circuit-switched and packet-switched traffic (e.g., voice traffic, data traffic, etc.) between mobile stations and other endpoints, which can be another mobile station or an endpoint connected to a network such as a public-switched telephone network (PSTN) or a packet data network (e.g., local area networks, the Internet, and so forth). Examples of wireless communications networks that support communication of packet-switched traffic include those that operate according to the GSM (Global System for Mobile) or UMTS (Universal Mobile Telecommunications System) standards, as defined by the Third Generation Partnership Project (3GPP).
Current GSM/UMTS networks include a GPRS (General Packet Radio Services) core network for providing packet services, such as Internet Protocol (IP) packet services. The GPRS core network includes a Serving GPRS Support Node (SGSN) and a Gateway GPRS Support Node (GGSN). The GGSN is a gateway between the GPRS core network and an external packet data network. In the uplink direction, the GGSN detunnels subscriber data traffic received from the SGSN and sends out data packets (such as IP packets) over the external data network. In the downlink direction, the GGSN receives IP packets from the external data network and tunnels subscriber data traffic to the SGSN. The SGSN performs various tasks, including mobility management, session management, billing, and so forth.
A mobile communications network includes coverage areas (referred to as cells) that are supported by respective radio access networks. The radio access networks include respective base transceiver stations (BTSs) or access points (APs) for wirelessly communicating with mobile stations in respective coverage areas. The radio access networks also include a radio network controller (RNC) or base station controller (BSC) that is connected to a respective BTS or AP.
When a mobile station moves from one coverage area to another coverage area, a handover procedure is performed to transition the mobile station between the different coverage areas. The transition of the mobile station between the coverage areas involves a transition between different radio access networks (from a source radio access network to a target radio access network) and possibly between different SGSNs (from a source SGSN to a target SGSN).
During a handover procedure, delays in communicating traffic data to a mobile station may result from the fact that a core network may not know which SGSN and/or RNC is supporting communications with the mobile station that is moving between coverage areas. For example, packets sent by the core network to a mobile station may experience extra delay due to data packets having to be forwarded from a GGSN through an SGSN to a source RNC, and then from the source RNC to a target RNC. The extra delay in the communication of traffic data from the core network to a mobile station while the mobile station is transitioning between coverage areas may cause service interruptions for latency-sensitive applications such as voice-over-IP (Internet Protocol) communications or other forms of real-time communications in wireless communications networks.